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BQ40Z50-R2: TD & FD vs CELL_TERM

Zhihan Zhang
Expert 1100 points
Part Number: BQ40Z50-R2

Hi TI Team,

For my current 40z50 design, I'm using CELL_TERM = 0 for pack based termination. However TD & FD are both cell based. So that mean in most cases, TD and FD may set earlier than cell stack based discharge termination. Do you know if this will be an issue during application since there is some difference between CELL_TERM (cell stack based) and TD/FD (cell based)?

Thanks,

Zhihan

  • 0
    TI__Guru** 105760 points

    Hello Zhihan,

    The TD and FD flags can be set with either a voltage threshold or RSOC threshold (it's RSOC by default) You can check section 4.7 Charge and Discharge Termination Flags

    I don't think it will make a difference whether you have CELL_TERM = 0 or 1.

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Expert 1100 points

    Hi Wyatt Keller,

    Thanks for your reply!

    I think my question is why there is no cell stack based FD/TD?

    For example, say we have 3 series battery with Term Voltage = 9V, FD/TD = 3V/cell. It could happened that FD/TD set earlier than reach Term Vpltage. Since FD/TD is cell based while CELL_TERM = 0 is cell stack based. So there is some asynchronization in between. In this case, when we use FD/TD to inform the host to terminate discharge, the inform is actually earlier since cell stack voltage has not drop to 9V yet?

    Thanks,

    Zhihan

  • 0 in reply to Zhihan Zhang
    TI__Guru** 105760 points

    Hello Zhihan,

    You're correct, that could be the case if the cells are significantly imbalanced. To make sure the FD and TD bits set you would need to make sure they are high than the min term voltage with whatever voltage delta. Or you can use the RSOC method which is not cell based.

    Sincerely,

    Wyatt Keller